Hello,
I bought a 2003 r53 (105K) a few months ago. I found Mod Mini's youtube channel and have done a lot of tune up and maintenance. The car seems to be running really well now, and no more oil drips on the driveway. The old cam lobes were wearing down, so I put a new stock one in and had valve seats cleaned up.
However, when driving it seems like the power is rather flat in the mid range, a little before the super charger kicks in. Is this normal? Can it be tuned out?

 

Do you have a boost gauge? Boost is developed very differently with a supercharger from a turbo. With a turbo, exhaust volume makes the compressor compress air and boost is regulated by the wastegate. The Eaton supercharger outputs one unit volume of air each rotation, so you need to spin it faster to get more boost. The inherent inefficiencies of working in the real world seem to limit boost.

Having said that, there isn't a 'mid range before the sc kicks in'. The boost rises proportionally from about 7psi at 3000rpm to 12psi around 6000rpm (from memory). That means you don't get that kick in the back urgency like a turbo car coming on boost, it is just a surge forward getting faster the faster you go.

Does that sound like what you are experiencing? If so, it is a weakness of constant volume superchargers. You could change to a Whipple (I think), they are a crank driven compressor like a turbo, or maybe the RMW upgrade is like that. Or you could get a turbo for it, it has been done and they make some serious power but is pretty expensive and no one who I have seen do it thinks they would do it again. Or you can enjoy it the way it is meant to be enjoyed and learn to love the foibles and sc whine!

James

 

the power will feel flat, its using a blower, just take a look at our torque curve, preety much even from 3400 - 5800 rpm. the blower is a fixed rate of moving air... .7L per revolution which is driven off the crank. so at any rpm the air flow will be the same. a blower will give the flattest torque curve out of any forced induction. centrifigal s/c will have a torque curve that increases into the rev range due to air speed increasing and being belt driven. a turbo will have the surge of torque where the boost builds. which then can taper off or build depending on the size and efficiency of the turbo.


so in a word you should have the most shove at those rpm if you bring up there slowly, then matt it. but once in it, it will feel linear. no tune unless you have throttle restrictions (why???) will give you that feeling.


or your feeling of torque could be a boost leak, hard to tell since im not in your car =D


and the fact of a supercharger is, you can build boost at idle, once the engine has no vacuum through the manifold a bypass valve opens and starts feeding the SC into the intake which is your boost. theorectically if you don't have a pulley you can have 6-8 psi revving while not moving. which you cannot do in a turbo unless you have an anti lag tune

 

The first thing I think of is this - Have you looked at the bypass valve to see if it is opening and closing properly? No broken spring? May also be a good idea to reset all the adaptations. The engine adjusted for the old arrangement. You want to reset that...

 

So, what does a 15% reduction pulley do, just increase the amount of boost at all RPMs? I was thinking about installing one of those to give it a little more pull.
I looked into the bypass valve, that might describe the feel I'm getting. I'd say the flat spot is around 3K. I'll check that in the morning and see if the spring feels good.

 

About 2.5- 3k is about where the bypass valve closes....the transition tends to be flat...even has a bit of a feedback issue on some cause causing a yo-yo....
It has a spring and a vac line to make it do its thing....
Purpose of it is to let the motor run without boost at lower rpms,like cruise (hint,look at the engine rpm at typical cruising speeds unless you keep it wound up) to increase mpg...if you keep this in mind, a r53 can do 30 mpg with a 200+ HP tune...I did routinely in commuting.
Valves made post 2005 had a stiffer spring, as does the DT tuned version (stiffer still) ....
A 15% pulley or even a 17% brings on boost at lower rpms (I ran a 17%)...and yes it does help a bit...giving you more boost at lower rpms...
The desgin of the the motor makes for kinda low tq...so a fairly heavy flywheel is used to help too...keep this in mind if you consider going to a lighter one if you get a clutch....